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Working with experts in child development, the mom of three — who was first inspired while taking parenting classes as a new mother — founded Whole Child International, a nonprofit dedicated to teaching caregivers and government officials how to create a more loving and nurturing environment for the children in their care.

“Simply by ensuring that children have quality primary-care relationships, they will grow stronger,” says Spencer, who is one of 25 Women Changing the World featured in this week’s issue of PEOPLE. “This is absolutely implementable today — the shift can happen with very little resources, and the impact is huge.”

Karen Spencer in El Salvador in 2016.

Scott Chamberlin/Whole Child International

From orphanages to early childcare centers to foster care, WCI educates caregivers about children’s developmental needs at every age and stage and turns everyday tasks like bath and meal times into bonding experiences. Caregivers are taught how to create memory books for each child — celebrating first steps, first words, birthdays and more — to help deepen the connection, while also providing the children with a sense of individuality and identity.

“At Whole Child, our most important founding principle is that relationships are at the center of everything we do,” says Spencer, 45, who is married to Princess Diana’s brother, Charles, 9th Earl Spencer. WCI held its inaugural gala in Los Angeles on Oct. 26, and the event included a charity auction of two limited-edition versions of Charles Spencer’s 1997 eulogy for Diana as well as a stay at the family’s ancestral estate, Althorp.

By making changes to emphasize connective relationships, WCI has seen remarkable health gains, including a 47 percent increase in children’s heights and a 37 percent increase in weight — with no changes in diet.

“I feel like the real impact has yet to come,” says Spencer.”This has been great, but now we’re scaling up. What I would like to see in my lifetime is that all of the things that we’re teaching and all of the principles that we’re putting forth become so mainstream that it’s widely understood that of course you wouldn’t rotate children from one caregiver to the next, that parents are supported and understand the importance of connection.”

Ultimately, she says, “I want to ensure that every child has the experience of a loving long-term relationship, a connection that sets them up to be successful and the intimacy they need to be productive members of society.”

As for the challenges along the way, “starting a nonprofit is not easy,” she says, “but I don’t really listen to a lot of naysayers, and I try to surround myself with people who are accomplishing amazing things.” And she offers this piece of advice to her younger self: “Relax. Trust your gut. I did, but I wish I had not stressed about it.”